[IOT-2359][IOT-2360][IOT-2364] Separate provisioning with DOS

[IOT-2359][IOT-2360][IOT-2364] Separate provisioning with DOS

Restore functions removed in https://gerrit.iotivity.org/gerrit/#/c/19931/
Add NULL checking for pDev2 in SRPProvisionCredentialsDos

Change-Id: Icf3397247478c97c7029380aadcaa5dd89b42870
Signed-off-by: Dmitriy Zhuravlev <d.zhuravlev@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20387
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: dongik Lee <dongik.lee@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Reviewed-by: Jongmin Choi <jminl.choi@samsung.com>
Reviewed-by: Randeep Singh <randeep.s@samsung.com>